Polymer hydrogels are crosslinked (physical or chemical) three-dimensional networks, which is capable of absorbing solvents and swelling to a limited degree without dissolution. They behave like sort of solid and liquid. If under external stimuli such as temperature, pH, ionic strength, chemicals, pressure, light and electric field, a reversible change of shape and volume to hydrogels, they are called environment sensitive polymer gels or smart gels. Apart from hydrophilicity, hydrogels has a good permeability allowing water and oxygen to pass through. Furthermore, the hydrogels with suitable crosslinking density are tender and elastic, resembling soft tissue. Thus, hydrogels are widely applied as contact lens, tissue engineering scaffolds, artificial muscle, drug delivery carriers and wound dressings. Recently, considerable attention is being paid to developing hydrogel facial masks. A skin-care facial mask made from polyacrylic acid copolymer was reported. The compositions provide improved skin feel and residue characteristics together with excellent moisturizing, emolliency, rub-in and absorption characteristics (U.S. Pat. No. 5,420,118/1993). In Chinese Patent (CN 2462923), the preparation method of a reusable hydrogel skin-care patch was reported. It was composed of back membrane, hydrogel and protecting layer. The hydrogel layer can be loaded with a variety of nutrients for skin beauty. A poly(hydroxycarboxylic acid) hydrogel-based cosmetic patch was publicized in (U.S. Pat. No. 6,761,896/2004). The novel patch comprise of static magnetic layer and hydrogel layer encapsulating nutrients. The magnetic patch aids in reducing facial wrinkles and transdermal ingredient delivery.
The hydrogel-based facial masks developed to date are insensitive to surrounding stimuli. The nutrients loaded are delivered in a passive mode, and the weak mechanical strength inherent to hydrogel leaves much to be desired. It is noted that most of hydrogels applied as facial masks are devoid of antibacterial activity and have a poor skin affinity.
Poly(N-isopropylacrylamide, PNIPAAm) is a special polymer with a low critical solution temperature (LCST). While temperature is below 32-34°, PNIPAAm is dissolved in water; above this temperature, PNIPAAm precipitate in water. (K. C. Gupta, K. Khandekar, Temperature-responsive cellulose by Ceric(IV) ion-initiated graft copolymerization of N-isopropylacrylamide, Biomacromolecules 2003, 4:758-765). For crosslinked PNIPAAm hydrogel, it occurs to shrink at above LCST; while below LCST, it becomes swollen. The water absorbency and releasing rate of drug loaded can be tuned by varying temperature. This characteristic has been applied to temperature responsive drug delivery system and separation membrane. (A. Chilkoti, M. R. Dreher, D. E. Meyer, D. Raucher, Targeted drug delivery by thermally responsive polymers, Advanced Drug Delivery Reviews 2002, 54: 613-630). However, a heavy syneresis occurs to PNIAAm at above LCST, which is undesirable in facial mask. (C. K. Han, Y. H. Bae, Inverse thermally-reversible gelation of aqueous N-isopropylacrylamide copolymer solution, Polymer 1998, 39:2809-2814). Polyurethane (PU) hydrogel is known to be biocompatible, and exhibit sort of elasticity and high swelling degree. Much research has demonstrated that grafting hydrogel onto the surface of textile can raise the mechanical strength of gel itself. (J. O. Karlsson, P. Gatenholm, Solid-supported wettable hydrogels prepared by ozone induced grafting, Polymer 37: 4251-4256.).
As a naturally occurring basic polysaccharide, chitosan is biocompatible, non-toxic, and antibacterial. It was also shown to have a good skin affinity, cause no allergy and readily form membrane. (Z. T. Zhang, L. Chen, J. M. Ji, Y. L, Huang, D. H. Chen, Antibacterial properties of cotton fabrics treated with Chitosan, Textile Research Journal, 2003, 73:1103-1106). In view of the characteristics above, this invention aims to develop cellulose fabric-supported chitosan modified thermoresponsive NIPAAm/Polyurethane copolymer hydrogel for facial mask. The hydrogel layer can load a variety of nutrients such as vitamins, aloe extract. At body temperature, the hydrogel deswell to facilitate the release of nutrients and water.